So why replace the knee, the over riding reason is pain. Knee replacement is now becoming a more common operation than hip replacement in the UK due to the frequency of knee arthritis in the population.


Many factors play a role in the decision making process for knee surgery including age, activity restrictions, occupation and medical health. Typically surgery takes approximately one hour and requires an anaesthetic. The anaesthetist will discuss the options and advise which is most appropriate anaesthetic for an individual patient. Medications are provided to maintain comfort and maintain a low rate of infection.

Above: Xrays showing an arthritic knee before surgery and after replacement of the joint.

The surgical team operates in a strictly clean environment. Our operating theatres are designed to control the flow of air and increase the sterility of the environment. These ultraclean theatres have bacterial air filters and more than 300 air changes per hour, reducing the risk of infection. By comparison a normal operating theatre will have 10-12 air changes in an hour.


The skin is cleaned with an antibacterial solution and sterile drapes are applied. Along the front of the knee there will be a surgical incision tailored in size to allow safe and accurate implantation of the knee replacement. Using special instruments the surgeon will contour the bone so they precisely fit the artificial knee components. The new components are inserted and the knee is closed. A small plastic tube called a drain may be used to remove any excess blood collecting within the knee following surgery and a comfortable bandage will be applied. Rehabilitation and physiotherapy will usually commence the day after surgery.


Following knee replacement surgery the average length of stay in hospital is 4 days, although remember this is an average and you shouldn’t feel something is wrong if you have not achieved this target. Dissolving sutures can be used in the skin which do not require removal, although if alternative sutures or skin staples are used they will require removal approximately 10 days following surgery. Having left the hospital, you will continue with mobilisation and physiotherapy exercises as taught to you in hospital. Your surgeon will review your progress in the outpatient clinic approximately 6-12 weeks following surgery. Although the strength, comfort and confidence improve rapidly over the first few months, your knee will continue to improve for up to a year.



Some patients have arthritis affecting a single compartment of the knee and may be suitable for a partial knee replacement called unicompartmental. The most usual site for this is the medial (inner) compartment of the knee.


Following this surgery the recovery is more rapid and the knee function more normal than a full replacement. However, the longer term success is not as good as a full knee replacement given that arthritis may progress to the other knee compartments causing symptoms to recur.

Benefits and risks of knee replacement

Although pain relief is the main aim following surgery, improved function and correction of limb deformity due to arthritis are associated benefits. Although uncommon, it is an unfortunate fact that not all operations and their recovery go without complication. The main risks associated with knee replacement include can be described as those generally related to surgery and those risks which are specific to knee replacement.


General risks do increase with age due to an increasing frequency of associated medical conditions affecting the heart, lungs, urinary and gastrointestinal tract. Surgery stresses the body and can cause otherwise dormant conditions to become problematic. Urinary retention is the most common of the general risks and presents with difficulty passing urine after surgery. A urinary catheter is passed into the bladder, which remains in place typically for a few days.


Blood Clots (DVT / PE)

To minimise a blood clot we encouraging early mobility together with medications to thin the blood and mechanical pumps to aid blood flow in the limbs while at rest. A deep vein thrombosis or ‘DVT’ is a blood clot occurring in the deep veins of the leg in approximately 5% of patients. A pulmonary embolism or ‘PE’ is a more serious condition occurring when a blood clot travels to the veins in the lung in 1% which can be life threatening for 1 in 1000 patients.


Serious deep infection occurs in 0.5% and often requires further multiple surgeries in an attempt to eradicate the infection. Superficial infections are more frequent perhaps 3-5% and can be associated with delayed wound healing or a collection of blood beneath the skin (haematoma). The rates of MRSA and Clostridium infection in the orthopaedic hospital are zero.


Altered sensation on the side of the knee – very common

Nerves in the skin are injured through the unavoidable surgical incision. This leaves an area of reduced sensation on the outer aspect of the knee. The area of altered sensation often improves in the months following surgery, although an area of abnormal sensation always persists.


Avoidance of kneeling 50%

There are many reasons people choose not to kneel on their replaced knee although your surgeon usually doesn’t mind if you want to do this.

Knee Stiffness – uncommon

After rehabilitation the replaced knee should bend at least to a right angle if not more. A knee which bends less than this can cause difficulty for the patient with some activities. Some conditions are associated with a higher risk of stiffness following surgery such as diabetes and the medication warfarin for example. However despite the surgery going well, many patients have no obvious predisposing cause. Treatment with manipulation of the joint under anaesthetic can help, although the result is often unpredictable.


Loosening and Fracture

Dependant on patient age, approximately 95% of knee replacements last for 10 years. All artificial joints wear with use and so eventually will loosen and require redo (revision) surgery. With severely worn artificial joints there is often loss of surrounding bone which can predispose to a fracture.


Major Nerve damage – rare

Nerve injury causing reduced sensation or weakness in the foot can occur but is rare.


Other rare complications <1%

Although there a many other described complications they are rare. Some of these include fat embolism, knee dislocation, patella fracture, major blood vessel injury, heart attack, stroke and mortality.